Iron blast furnace fuel injection



July 27, 1965 J.-W. CARLSON IRON BLAST FURNACE FUEL INJECTION Filed Jan. 15. 1962 United States Patent 3,197,305 IRON BLAST FURNACE FUEL INJECTION John W. Carlson, Pueblo, Colo., assignor to The Colorado Fuel and Iron Corporation, Denver, (1010., a corporation of Colorado Filed Jan. 15, 1962, Ser. No. 166,184 4 Claims. (Cl. 75-42) This is a continuation-in-part of my copending application Serial No. 96,171, filed March 16, 1961, now

U.S. Patent No. 3,166,621, granted January 19, 1965.

This invention relates to the production of iron in the blast furnace, and has for its object the provision of an improved process for carrying out the heating and reducing of the charge. More particularly, the invention aims to eliminate a substantial part of the coke usually used to heat and reduce the iron, and to this end provides an improved process for charging into the blast furnace through the tuyeres or nozzles a suspension of powdered solid carbonaceous fuel in a liquid hydrocarbon fuel.

The invention achieves an effective charging through the tuyeres or nozzles of solid carbon into the blast furnace resulting in a decrease in the amount of coke, and the utilization of a variety of fuels not heretofore practical for blast furnace operations.

For many years it has been the practice to charge the blast furnace with a mixture of iron ore, limestone, and metallurgical coke. It has been proposed to use fuel oil and other hydrocarbon liquids as a substitute or supplement for the coke. Combustible gases and liquid fuels have been injected into the blast furnace through nozzles to react with the air and yield heat and reducing gases, the objective being to increase the ore to coke ratio in the charge of the furnace and supplement the coke. The temperature resulting from the reactions at the tuyere zone, however, is a critical factor in the performance of the furnace, particularly with regard to the grade of iron produced. Hydrocarbons have a cooling effect on the tuyere zone, because the release of hydrogen gas is endothermic. The mass of the relatively cool reactants also tends to absorb heat from the tuyere zone. Accordingly, the proposed gaseous and liquid fuel substitutes for coke have not been fully successful. Such substitute fuels have also caused difiiculties in preventing the tuyere burners from becoming fouled, and in maintaining a proper balance in the combustion, thermal and metallurgical reactions.

In the process of this invention solid particulate carbon such as raw coals, both anthracite and bituminous; gilsonite; coke produced from coal, petroleum, or gilsonite, and chars are suspended in the liquid fuel and charged into the blast furnace. The solid carbon must be in such a state of subdivision that it will remain in suspension and also feed through the nozzles or tuyeres.

The carbon is reduced to any suitable state of subdivision, preferably powdered, but may be sized to pass through a screen of up to inch mesh.

The liquids suitable for suspending the solids include: heavy oil, for example bunker-C or No. 6 fuel oil; coal tar, products of the coking process; composite of the coking process, and mixtures or blends of the lighter fractions of the petroleum and coal distillation products with the heavier oil or tar to obtain a liquid having the desired viscosity.

In accordance with the process of this invention, the powdered solid fuel is mixed with the liquid fuel to form a suspension of the solid in the liquid which is charged through suitable nozzles or tuyere burners into the blast ice furnace. The invention advantageously uses hydrocarbons having the minimum amount of hydrogen and the highest permissible amount of carbon in which the solid fuel is suspended as in a slurry.

This invention is based on my discovery of a combination of solid carbon particles and a hydrocarbon liquid having such properties with respect to the specific gravity and particle size of the solid carbon that the particles are held in uniform or stable suspension for appreciable periods without agitation. The solid carbon is mixed with a liquid hydrocarbon having such specific gravity and preferably also such viscosity that the particles remain in suspension so that the liquid-solid fuel composition can be delivered to a header, Without settling or plugging therein, from which all of the tuyeres can be supplied. This avoids the difiicult problem of supplying each tuyere with a composition which requires agitation to hold the carbon particles in suspension. Each tuyere is accordingly supplied with thesame composition and without the use of complicating agitating equipment.

The fluidity characteristics of the slurry are regulated to achieve ease of mixing and pumping and the degree of viscosity required to hold the solids in suspension as the slurry is distributed to the tuyeres. These requirements are fulfilled by reducing the differential gravitational and accelerational forces which tend to separate the solids from the liquids. The fluidity of the slurry depends primarily on the viscosity of the liquid phase. The liquids are selected and blended to obtain the desired viscosity characteristics, and the operation of the system is controlled by regulating the temperature of the mixture. In general, the viscosity of the liquid increases as the carbon content of the liquid increases. For the heavy hydrocarbons, the optimum viscosity is obtained at a temperature generally between and F. The fluidity of the liquid-solid fuel slurry is also dependent upon the nature of the solids and the percent of solids in suspension.

The specific gravities of the solids of interest are approximately as follows:

Apparent specific gravity Char 0.98 Coke (coal) 1.01.05 Coke (petroleum) 1.3 Coke (gilsonite) 1.0-1.05 Coal (anthracite) 1.3-1.5 Coal (bituminous) 1.3-1.5 Gilsonite 1.3-1.5

The specific gravities of the liquids vary inversely with the carbon content as shown by the following:

The relation of the specific gravities of the solids and the liquids can be selected to be very close. A suspension of char in fuel oil, for example, exhibits very little tendency to settle; and char can actually float in coal tar. Even the heavier materials, the coals, are not difficult to keep in suspension in a heavy liquid by keeping the slurry in motion. The suspension becomes increasingly uniform as the percentage of solids is increased, because the interaction of the particles hinders the settling rate.

The only limitation on the amount of solids in the liquid is the fluidity required for the slurry to, flow through the pipes leading to and in the burners. The optimum range is 40 to 50 percent of solids, with a permissible upper limit of about 60 percent of solids. It is possible also to use slurries having a lower solid content. The liquid-solid fuel mixture may be blown through a plurality of simple nozzles such as'% inch pipes into suitable contact with an oxygen-containing gas. Any suitable type of burner for burning heavy fuel oil may be used, preferably burners which effect an atomizing of the liquid in a stream of air, oxygen-enriched air or commercial oxygen. The fuel mixture may be under a pressure of from 30 to 100 p.s.i.g. to charge the fuel mixture through the nozzles under high velocity into contact with the air or oxygen-containing gas.

In one aspect of the invention, the liquid-solid fuel mixture may be used in combination with natural gas in the operation of the blast furnace. To this end the natural gas may be blown through the burner carrying the liquid-solid fuel mixture. The natural gas may also be used as a carrier for suspended pulverulent solid fuel of the types described, preferably in a very time state of subdivision. In one aspect of my invention the fuel mixture and natural gas may be charged through a fuel burner of the type described in my said copending application Serial No. 96,171. In using a burner of that type, the liquid-solid fuel mixture is charged into a surrounding stream of natural gas and this accomplishes not only dispersion of the liquid-solid fuel mixture in the gas, but forms an envelope of gas surrounding the pipe carrying the fuel mixture which prevents overheating of the fuel mixture in the pipe and the deposition of carbon from the fuel mixture. I may carry the liquid-solid fuel mixture through a relatively small pipe mounted within a larger gas pipe and have their discharge openings at about the same lace so that these fluids, released under pressure, become intermixed preferably just in advance of the point of combustion and are directed into the axis of an oxygen-containing gas which burns the fuel. Where natural gas is used without suspended carbon it can serve to decrease the temperature near the tuyeres due to its endothermic reaction in decomposing. This dispersion of the liquid-solid fuel mixture in the natural gas results in an effective mixing with the air and good combustion.

The most important benefit from the liquid-solid fuel mixture is achieved in the supply to a blast furnace of an effective blend of a liquid and solid particle having a high ratio of carbon to hydrogen and hence high heat capacity.

The burner of my said patent application is illustrated in the accompanying drawings in which FIG. 1 is a side view, partly in section, of the burner installed in a blast furnace, and

FIG. 2 is a fragmentary enlargement of the burner of FIG. 1.

The complete burner 1 is mounted in the water cooled tuyere opening 2 in the wall 3 of a blast furnace. It is to be understood that each tuyere opening will have a similar burner. As illustrated, the burner is an adaptation of the usual tuyere system for blowing air into the blast furnace consisting of a tuyere 4 which has an annular space 5 for cooling water forced in through pipe 6 and out through pipe 7. The air duct 8, known as a blow pipe, is connected by the flanges 9 to the air supply pipe 10 which leads to the usual bustle pipe (not shown). The sighting device 11 is mounted in the pipe 10.

The fuel nozzle 15 comprises an outer pipe 16 for the supply of natural gas when. it is desired to use such gas, and a concentric smaller inner pipe 17 for the liquidsolid fuel mixture. This nozzle is water cooled, advantageously by mounting it in the water-cooled tuyere 4 as shown. This may be done by welding, or by casting a copper tuyere 4 around a Monel metal or other alloy or copper pipe 16.

The nozzle pipe 16 is connected to the natural gas supply pipes 18 and 19. The pipe 18 has an attached packing gland 20 through which the liquid-solid fuel mixture supply pipe 21 passes and is either connected to, or is continuous with, the pipe 17. In an effective burner construction, the pipes 13 and 19 are preferably about A in diameter and pipe 16 may be the same size or a little smaller. These pipes may be of steel or copper. The pipes 17 and 21 are smaller in diameter. The gland 20 may be a pipe union having the copper tube 21 welded to the union half, as shown, to form a tight connection. The pipe 21 is connected to the header or manifold pipe 25 which receives the liquid-solid fuel slurry from a pump (not shown). It will be noted that the end of the nozzle 15 is so constructed that it projects into the space within the tuyere 4 and in the air stream in such a manner that the mixture is directed into the center of the air stream. The pipe 17 preferably ends short of the end of pipe 16.

The aforementioned nozzle is effective for carrying out a process of the invention in which natural gas is used. However, I may carry out another important process of the invention in a variation of this burner in which natural gas is not used. To this end I may change the construction of the burner by eliminating the small tubes 17 and 21 and pipe 18 and plug the T 24 in which case all the liquid-solid fuel mixture is charged from the header directly into the pipes 19, 18 and 16. In this operation the pipe 1 5 is the nozzle for the liquid-solid fuel mixture.

It is advantageous to provide a temperature measuring device on the burners and to this end the bimetallic element 2,2 is in the form of a band attached to the air pipe 3 and the electric wires 23 lead to a suitable temperature recording or signal device (not shown).

In carrying out a blast furnace combustion process of the invention with the burner illustrated, I prefer to use a heavy oil or bunker-C distillation residue because of their high carbon content and low cost and carbon particles closely approximating the specific gravity of the oil. \Vhen using a heavy or viscous iuel it should be heated to decrease its viscosity and facilitate dispersing the solid fuel particles therein. I prefer to heat this liquid to a temperature of from 120 F. to 250 F. and to discharge it at a pressure varying from 20 to 25 p.s.i.g.

When carrying out an operation in which natural gas is used, the preferred ratio of liquid-solid fuel mixture to natural gas is from 0.5 to 4 pounds of the mixture per pound of natural gas. The methane or natural gas is preferably passed through pipes 19, 18 and 16 as an envelope surrounding pipe 17. This gas is preferably used at normal temperatures and under a preferred pressure of from 30 to p.s.i.g. The liquid-solid fuel mixture and gas impinge upon each other at the end of nozzle 15 and this results in an effective dispersion and intermixing with the air in tuyere 4. The liquid component is accordingly atomized and this results in effective combustion. This liquid-solid fuel mixture can be supplied to the burner over long periods without plugging the nozzle 15 because the surrounding layer of cooler natural gas in pipe 1-5 serves as a thermal barrier and prevents the heating of pipe 17 to a pointwhere the oil is cracked with resulting carbon deposits which can plug the nozzle.

In a variation of carrying out the process in which natural gas is used, I may suspend in the natural gas a finely divided solid such as coal or coke ground to pass through a 6 mesh screen. The natural gas may carry from 1 to 5 ounces of coal per cubic foot.

I have made the surprising discovery that the liquidsolid fuel mixture can be charged into the blast furnace and burned with air enriched with oxygen containing up to 35 percent of oxygen. It has been the prevailing belief heretofore that such. an amount of oxygen would be difficult to use, if not actually dangerous.

I claim:

1. In the operation of a blast furnace for producing iron of the type having a plurality of tuyeres, each tuyere having a fuel nozzle therein and a pipe system for supplying fuel to the nozzle, the improvement which comprises charging iron ore, limestone and coke into the furnace, the amount of coke being insuflicient to reduce all of the iron ore, blowing through the nozzles a liquid-solid fuel mixture consisting of solid carbon particles suspended in a hydrocarbon liquid fuel selected from the group consisting of bunker-C oil, coal tar and mixtures thereof, the specific gravities of the solid carbon and hydrocarbon liquid fuel being approximately the same, said fuel mixture being forced through the pipe system and blown out of the nozzles into contact with an oxygen-containing gas being blown through the tuyeres, said fuel mixture being charged into the furnace in at least: an amount sufficient to reduce the iron ore unreduced by coke.

2. In the process of claim 1 charging through the nozzle a jet of natural gas into impinging contact with the fuel mixture where the fuel mixture contacts the oxygen-containing gas.

3. The process of claim 1 in which the solid carbon is a solid carbon of the group consisting of coal, coke, gilsonite and char.

4. In the process of claim 1 heating the fuel mixture to increase its fluidity prior to forcing it through the pipe system and blowing it out of the nozzles.

DAVED L.

References Cited by the Examiner UNITED STATES PATENTS 9/ 85 Weber 7542 19/21 Carstens 7542 12/24 Kirby 7542 6/29 Danforth 7543 1/34 Brassert 75-42 5/ Toulmin -42 X 11/63 Sanders 75-42 12/63 Reichl 75-42 FOREIGN PATENTS 1904 Great Britain. 6/21 Great Britain.

RECK, Primary Examiner.

RAY K. WINDHAM, WINSTON A. DOUGLAS,

Examiners. 

1. IN THE OPERATION OF A BLAST FURNACE FOR PRODUCING IRON OF THE TYPE HAVING A PLURALITY OF TUYERES, EACH TUYERE HAVING A FUEL NOZZLE THEREIN AND A PIPE SYSTEM FOR SUPPLYING FUEL TO THE NOZZLE, THE IMPROVEMENT WHICH COMPRISES CHARGING IRON ORE, LIMESTONE AND COKE INTO THE FURNACE, THE AMOUNT OF COKE BEING INSUFFICIENT TO REDUCE ALL OF THE IRON ORE, BLOWING THROUGH THE NOZZLES A LIQUID-SOLID FUEL MIXTURE CONSISTING OF SOLID CARBON PARTICLES SUSPENDED IN A HYDROCARBON LIQUID FUEL SELECTED FROM THE GROUP CONSISTING OF BUNKER-C OIL, COAL TAR AND MIXTURES THEREOF, THE SPECIFIC GRAVITIES OF THE SOLID CARBON AND HYDROCARBON LIQUID FUEL BEING APPROXIMATELY THE SAME, SAID FUEL MIXTURE BEING FORCED THROUGH THE PIPE SYSTEM AND BLOWN OUT OF THE NOZZLES INTO CONTACT WITH AN OXYGEN-CONTAINING GAS BEING BLOWN THROUGH THE TUYERES, SAID FUEL MIXTURE BEING CHARGED INTO THE FURNACE IN AT LEAST AN AMOUNT SUFFICIENT TO REDUCE THE IRON ORE UNREDUCED BY COKE. 